Longwall mining is one of the most efficient methods for underground coal recovery where a large panel of coal, bounded by roadways (gateroads) is extracted by means of a mechanised shearing apparatus. The gateroads provide access for equipment and personnel and are essential to the longwall mining process.
The normal process of longwall mining involves removing product from the face of a product panel while progressively retreating in the direction of a gateroad. Thus, as the mining progresses, a mining machine installation moves down a gateroad and carries with it a shearing apparatus that shears product from the product panel. The movement into the product panel in the direction of the gateroad is termed “retreat”.
The gateroads are usually cut into the strata before mining of the product from the product panel and product seam, and the gateroads are intended to have long term structural integrity. The process of removing the product from the product panel can, however, introduce large stresses in regions surrounding the gateways. These stresses, in turn, may produce local movements to the surfaces of the gateroads such as fracturing, guttering, spalling, and cracking which are usually readily detected by the naked eye and can be suitably addressed. The stresses, however, produce other local features in the gateroads which can lead to deformation of the overall gateroad structure over time. This deformation is known as convergence. Convergence represents a subtle and dangerous form of stress-induced gateroad deformation because it usually occurs at a rate which is imperceptible to the unaided human eye and this makes it difficult to detect. Failure to note gateroad convergence can lead to collapse and failure of the gateroads themselves and can result in severe safety hazards to personnel and equipment.
Convergence has been determined in the past by use of an extensometer device which is placed at specific points in the gateroad to measure the distance between the gateroad roof and the gateroad floor at different time instants. The method is dependent on manual operation of the extensometer device and is invasive, and often is required to be performed in a hazard area. It is not until after the manual measurement is made with the extensometer device that the human operator can ascertain that there has been excessive convergence resulting in a hazardous situation. Further, such methods can be obstructive to the normal passage of the gateroad traversing structure of a mining machine installation used for mining product from the product face.
Objects and Statement of Invention
It is therefore an object of the present invention to attempt to provide a method and apparatus for monitoring gateroad structural change that overcomes one or more of the aforementioned problems.
According to a first broad aspect of the invention there is provided                a method of determining gateroad structural change in a mining operation comprising:        using a gateroad profile scanning sensor at a position of a gateroad to scan generally orthogonally to a direction of the gateroad and obtaining a first profile scan of surfaces of the gateroad and storing information of that first profile scan in a memory,        
at a later time obtaining a second profile scan of surfaces of the gateroad generally orthogonal to the direction of the gateroad at a position in the gateroad that generally coincides with the position where the first profile scan was made, and obtaining information of that second scan,
registering the stored information of the first profile scan with information of the second profile scan,
noting from the registered information of the first profile scan and the second profile scan any structural change of the surfaces of the gateroad.
According to a second broad aspect of the invention there is provided an apparatus for determining gateroad structural change in a mining operation comprising                scanning apparatus for providing information of a first profile scan of surfaces of a gateroad at a position of a gateroad and generally orthogonal to a direction of the gateroad, and at a later time information of a second profile scan of surfaces of a gateroad generally at the same position of the gateroad as the first scan and generally orthogonal to a direction of the gateroad,        a memory store for storing information of a first profile scan,        a registering means for registering the profile scan information stored in the memory store with information of the second profile scan position where the second scan coincides with the position where the first scan was made,        a scan difference processor to permit noting of differences in information of first scan and the second scan, whereby a gateroad structural change can be determined        